Feasibility of a Novel Sparse Orthogonal Collimator-Based Preclinical Total Marrow Irradiation for Enhanced Dosimetric Conformality

Exploring Automated Contouring Across Institutional Boundaries: A Deep Learning Approach with Mouse Micro-CT Datasets

Image-guided mouse irradiation is essential to understand interventions involving radiation prior to human studies. Our objective is to employ Swin UNEt Transformers (Swin UNETR) to segment native micro-CT and contrast-enhanced micro-CT scans and benchmark the results against 3D no-new-Net (nnU-Net). Swin UNETR reformulates mouse organ segmentation as a sequence-to-sequence prediction task, using a hierarchical Swin Transformer encoder to extract features at 5 resolution levels, and connects to a Fully Convolutional Neural Network (FCNN)-based decoder via skip connections. The models were trained and evaluated on open datasets, with data separation based on individual mice. Further evaluation on an external mouse dataset acquired on a different micro-CT with lower kVp and higher imaging noise was also employed to assess model robustness and generalizability. Results indicate that Swin UNETR consistently outperforms nnU-Net and AIMOS in terms of average dice similarity coefficient (DSC) and Hausdorff distance (HD95p), except in two mice of intestine contouring. This superior performance is especially evident in the external dataset, confirming the model's robustness to variations in imaging conditions, including noise and quality, thereby positioning Swin UNETR as a highly generalizable and efficient tool for automated contouring in pre-clinical workflows.

Total marrow irradiation reduces organ damage and enhances tissue repair with the potential to increase the targeted dose of bone marrow in both young and old mice

Total body irradiation (TBI) is a commonly used conditioning regimen for hematopoietic stem cell transplant (HCT), but dose heterogeneity and long-term organ toxicity pose significant challenges. Total marrow irradiation (TMI), an evolving radiation conditioning regimen for HCT can overcome the limitations of TBI by delivering the prescribed dose targeted to the bone marrow (BM) while sparing organs at risk. Recently, our group demonstrated that TMI up to 20 Gy in relapsed/refractory AML patients was feasible and efficacious, significantly improving 2-year overall survival compared to the standard treatment. Whether such dose escalation is feasible in elderly patients, and how the organ toxicity profile changes when switching to TMI in patients of all ages are critical questions that need to be addressed. We used our recently developed 3D image-guided preclinical TMI model and evaluated the radiation damage and its repair in key dose-limiting organs in young (~8 weeks) and old (~90 weeks) mice undergoing congenic bone marrow transplant (BMT). Engraftment was similar in both TMI and TBI-treated young and old mice. Dose escalation using TMI (12 to 16 Gy in two fractions) was well tolerated in mice of both age groups (90% survival ~12 Weeks post-BMT). In contrast, TBI at the higher dose of 16 Gy was particularly lethal in younger mice (0% survival ~2 weeks post-BMT) while old mice showed much more tolerance (75% survival ~13 weeks post-BMT) suggesting higher radio-resistance in aged organs. Histopathology confirmed worse acute and chronic organ damage in mice treated with TBI than TMI. As the damage was alleviated, the repair processes were augmented in the TMI-treated mice over TBI as measured by average villus height and a reduced ratio of relative mRNA levels of amphiregulin/epidermal growth factor (areg/egf). These findings suggest that organ sparing using TMI does not limit donor engraftment but significantly reduces normal tissue damage and preserves repair capacity with the potential for dose escalation in elderly patients.

An efficient rectangular optimization method for sparse orthogonal collimator based small animal irradiation

Objective.Intensity-modulated radiotherapy (IMRT) is widely used in clinical radiotherapy, treating varying malignancies with conformal doses. As the test field for clinical translation, preclinical small animal experiments need to mimic the human radiotherapy condition, including IMRT. However, small animal IMRT is a systematic challenge due to the lack of corresponding hardware and software for miniaturized targets.Approach.The sparse orthogonal collimators (SOC) based on the direct rectangular aperture optimization (RAO) substantially simplified the hardware for miniaturization. This study investigates and evaluates a significantly improved RAO algorithm for complex mouse irradiation using SOC. Because the Kronecker product representation of the rectangular aperture is the main limitation of the computational performance, we reformulated matrix multiplication in the data fidelity term using multiplication with small matrices instead of the Kronecker product of the dose loading matrices. Solving the optimization problem was further accelerated using the Fast Iterative Shrinkage-Thresholding Algorithm (FISTA).Main results.Four mouse cases, including a liver, a brain tumor, a concave U-target, and a complex total marrow irradiation (TMI) case, were included in this study with manually delineated targets and OARs. Seven coplanar-field SOC IMRT (sIMRT) plans were compared with idealistic fluence map based IMRT (iIMRT) plans. For the first three cases with simpler and smaller targets, the differences between sIMRT plans and iIMRT plans in the planning target volumes (PTV) statistics are within 1%. For the TMI case, the sIMRT plans are superior in reducing hot spots (also termedDmax) of PTV, kidneys, lungs, heart, and bowel by 20.5%, 31.5%, 24.67%, 20.13%, and 17.78%, respectively. On average, in four cases in this study, the sIMRT plan conformity is comparable to that of the iIMRT's with lightly increased R50 and Integral Dose by 2.23% and 2.78%.Significance.The significantly improved sIMRT optimization method allows fast plan creation in under 1 min for smaller targets and makes complex TMI planning feasible while achieving comparable dosimetry to idealistic IMRT with fluence map optimization.